Crawling The Deep Web
A vast amount of Web pages lie in the deep or invisible Web. These pages are typically only accessible by submitting queries to a database, and regular crawlers are unable to find these pages if there are no links that point to them. Google's Sitemaps protocol and mod oai are intended to allow discovery of these deep-Web resources.
Deep Web crawling also multiplies the number of Web links to be crawled. Some crawlers only take some of the -shaped URLs. In some cases, such as the Googlebot, Web crawling is done on all text contained inside the hypertext content, tags, or text.
Strategic approaches may be taken to target deep-Web content. With a technique called screen scraping, specialized software may be customized to automatically and repeatedly query a given Web form with the intention of aggregating the resulting data. Such software can be used to span multiple Web forms across multiple Websites. Data extracted from the results of one Web form submission can be taken and applied as input to another Web form thus establishing continuity across the Deep Web in a way not possible with traditional web crawlers.
Read more about this topic: Web Crawler
Famous quotes containing the words crawling, deep and/or web:
“You know, Frank, I’m beginning to get a new perspective on this crawling little animal known as man. Why a dog or a cat or a bird is cleverer than any human. They sense me immediately. But these shrewd detectives of yours—. Take away one of man’s senses and you render him helpless.”
—Lester Cole (1904–1985)
“We know not what it is, dear, this sleep so deep and still;
The folded hands, the awful calm, the cheek so pale and chill;
The lids that will not lift again, though we may call and call;
The strange white solitude of peace that settles over all.”
—Mary Mapes Dodge (1831–1905)
“Any newspaper, from the first line to the last, is nothing but a web of horrors.... I cannot understand how an innocent hand can touch a newspaper without convulsing in disgust.”
—Charles Baudelaire (1821–1867)